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All-polymer organic solar cells offer exceptional stability. Unfortunately, the use of bulk heterojunction (BHJ) structure has the intrinsic challenge to control the side-chain entanglement and backbone orientation to achieve sophisticated phase separation in all-polymer blends. Here, we revealed that the P–i–N structure can outperform the BHJ ones with a nearly 50% efficiency improvement, reaching a power conversion efficiency approaching 10%. This P–i–N structure can also provide an enhanced internal electric field and remarkably stable morphology under harsh thermal stress. We have further demonstrated generality of the P–i–N structure in several other all-polymer systems. Considering the adjustable polymer molecular weight and solubility, the P–i–N device structure can be more beneficial for all-polymer systems. With the design of more crystalline polymers, the antiquated P–i–N structure can further show …